This invention relates to improvements in pumps and in particular but not exclusively to improved performance and reliability of shaft fluid seals as used in impeller pumps.
In the field of impeller pumps which incorporate a single impeller on an overhung shaft, the shaft seal is often provided with a suitably shaped annular space around it commonly referred to as a seal chamber or balance chamber. One purpose of the seal chamber is to assist in conducting away heat generated by the shaft seal. The seal chamber must be of adequate capacity and of suitable shape to promote a sufficient degree of swirling to enable a necessary proportion of the heat generated by the shaft seal to be transferred into the pumped media during the passage of that pumped media from wearing ring to impeller balance holes.
Sometimes the swirling action in the seal chamber is assisted by a duct or multiplicity of duets which permit a portion of the outlet pumped media to be directed into the seal chamber in a manner conducive to the cooling of the shaft seal. Typically the ducts may be drillings or pairs of drillings each of which also may need to be tapped or plugged, or one or more external tubes or pipes to pipe connectors which require drilling and tapping and may be also plugging. The ducted pumped media is typically circulated back to the main pumped flow through conventional impeller balance holes.
However, many impeller pumps are called upon to be axially compact. As such there may be insufficient space for an effectively proportioned seal chamber. Also there may be insufficient space for wearing rings or, alternatively, no wearing rings may be fitted as a cost saving.
In such arrangements it is thought that fluid circulation is impeded because the whole mass of fluid between the impeller and pump head tends to rotate as a whole in the manner associated with a liquid annular seal. The resulting pressure differential available across each of the impeller balance holes is insufficient to promote the flow rate which is required for adequate shaft seal cooling.
Accordingly, the present invention seeks to avoid or at least mitigate certain problems in the prior art including the lack of cooling of the shaft seal in, for example, an axially reduced pump arrangement. One object of the invention is to increase fluid recirculation back into the main flow path of the pump thereby to effect cooling and/or recirculation of fluid in the region of the shaft seal.
One aspect of the present invention provides a fluid pump comprising a body housing a fluid pumping chamber having a rotatable pumping member, a drive shaft which passes through an aperture in the body into the pumping chamber to effect rotation of the pumping member in use, and a seal between the pump body and rotary shaft to inhibit fluid moving along the shaft out of the pumping chamber, characterised by a dividing shroud operably located between the seal and the rotatable pumping member to divide the seal chamber between the seal and the rotary pumping member. Preferably, the dividing shroud is stationary in use.
Beneficially, the dividing shroud is found to increase circulation of the pump fluid, especially around the seal.
Preferably, fluid inlet into the first portion of the divided seal chamber, which first portion is adjacent the seal, is provided. Beneficially, a pressure gradient exists across the fluid inlet, and indeed across the whole first portion of the divided seal chamber, thereby to effect fluid flow into the first portion of the seal chamber.
Preferably, the dividing shroud comprises a central aperture which operably surrounds the rotatable shaft in use. Preferably, the radius of the aperture is slightly greater than the radius of the shaft thereby to provide a fluid passageway between the first and second divided portions of the seal chamber. Preferably, the circular rim of the central aperture can comprise a lip. The lip can extend axially along the rotatable shaft. Preferably, the lip extends away from the seal.
Preferably, means for attaching the dividing shroud to the pump body are provided. For example, the shroud can comprise one or more apertures to enable co-operating locking means such as a threaded bolt and threaded sockets in the pump body to be used to attach the shroud to the pump body. Of course, threaded bolts can protrude from the pump body and nuts can be used to fasten the shroud onto the pump body in this reverse configuration.
The dividing shroud can comprise an attachment or retaining device for co-operating with part of the pump body. For example, the shroud can comprise an annular resilient clip which engages a lip on the pump body thereby to provide a mechanical/frictional attachment.
The fluid inlet to the first portion can comprise a series of fluid passageways in the pump body around the dividing shroud. For example, a series of passageways can be provided between a series of bosses, castellations, or crenallations in the pump body itself.
Another aspect of the invention provides a dividing shroud for a seal chamber of pump. Another aspect provides a flow or recirculation enhancer for increasing recirculation of the fluid or pumped medium past a shaft seal in a pump back into the main flow path between pump inlet and outlet. A further aspect provides a pressure enhancer for increasing fluid pressure in the vicinity of the seal, preferably taking it close to the fluid outlet pressure for the pump.
A yet further aspect of the invention provides a fluid pump comprising a body housing a fluid pumping chamber having a rotatable pumping member, a drive shaft which passes through an aperture in the body into the pumping chamber to effect rotation of the pumping member in use, and a seal between the pump body and rotary shaft to inhibit fluid moving along the shaft out of the pumping chamber, wherein the fluid pumping chamber comprises a seal chamber defined at least in part by the seal and the rotatable pumping member and wherein the pump further comprises means locatable within the seal chamber for effecting circulation of fluid over the seal and back into the main fluid pumping chamber in use.